4D-Printed PLA/PEG/Mg Gyroid Metamaterial Scaffolds: Mechanistically Tunable Degradation and Body-Safe Shape Transformation.

Smart bone scaffolds require body-safe actuation, controlled degradation, and early mechanical support. Here, gyroid scaffolds were fabricated by fused deposition modeling using a metamaterial approach to couple shape recovery with mechanistically tunable degradation. Polylactic acid (PLA) was plasticized with 10 wt % polyethylene glycol (PEG) to lower the glass transition temperature (Tg), while 2.5 and 5 wt % magnesium (Mg) particles were incorporated to regulate degradation, reinforcement, and biocompatibility. Thermal and viscoelastic analyses confirmed Tg reduction to ∼44 °C, enabling body-safe activation. PLA/10PEG/2.5Mg achieved the best shape-memory response, with a shape recovery ratio (Rr) of 90.4% within ∼71 s. Physicochemical and mechanical degradation tracking over 12 weeks revealed that PEG leaching, Mg corrosion, and gyroid interconnectivity synergistically promoted bulk-like degradation, yielding up to ∼600% higher weight loss and mechanical retention. Cytocompatibility further improved with Mg incorporation. This work establishes a mechanistic framework for codesigning degradation and shape recovery in 4D-printed PLA/PEG/Mg scaffolds.